Friction type draft gear assemblies are widely used in United States railroad industry to provide protection to a railroad car by absorbing shocks in both draft and buff conditions. These draft gear assemblies must meet various Association of American Railroads (AAR) requirements. In one aspect the draft gear must be capable of maintaining the minimum shock absorbing capacity during its service life required by AAR standard M-901-E to be at least 36,000 foot pounds. In the other aspect AAR mandates working action of such draft gear to be achieved without exceeding a 500,000 pound reaction pressure acting on the freight car sills in order to prevent upsetting the coupler shank. In yet another aspect, the draft gear must pass a drop hammer test meeting the endurance portion of the AAR standard M-901-G, which determines the shock absorbing capacity of the draft gear.
The commonly used draft gears, installed in alignment with a railroad car center, include a housing having a front and a rear portion. A compressible cushioning element is positioned within the rear portion of the housing. A friction cushioning element is adopted in the front portion of the housing. The draft gears further include a spring release mechanism for continuously urging the friction cushioning element outwardly from the compressible cushioning element thereby releasing such friction cushioning element after compression of such draft gear. The compressible cushioning element is typically either of an all spring configuration or of a spring and hydraulic assembly combination as taught in U.S. Pat. Nos. 3,358,698 and 5,152,409.
The draft gear employing a hydraulic assembly, enables a higher drop hammer capacity than an all spring design, as evident by the hammer test results, and is capable of shock absorbing capacity of about 70,000 foot pounds.
In some applications which are not subject to existing AAR regulations and standards, a higher protection to the railroad car prior to the draft gear using all of its travel is required, even though this protection is achieved at a higher reaction force then is allowed by the existing AAR standards. This higher protection requires the shock absorbing capacity of the draft gear to be slightly higher than 100,000 foot pounds.
It is further desirable to achieve such higher protection, in the most economical method of retrofitting existing draft gears.